High-low speed hoist valve



June 11, 1963 A. A. ROOD 3,093,116

HIGH-LOW SPEED HOIST VALVE June l1, 1963 A. A. ROOD HIGH-LOW SPEED HOIST VALVE 5 Sheets-Sheet 2 Filed April '7. 1960 if f4 NVENTOR. @f4/27 @gvd ATTORNEY `lune 1l, 1963 Filed April 7, 1960 5 Sheets-Sheet 5 INI/ENTOR.

@//227 @fnd United States Patent O 3,093,116 HIGH-LOW SPEED HOIST VALVE Alvin A. Rood, Willoughby, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Apr. 7, 1960, Ser. No. 20,743 13 Claims. (Cl. 121-38) This invention pertains to a fluid pressure system for controlling under various operating conditions a` fluid pressure-operated hoist or jack connected to a load and, in particular, to a system including a high-low speed hoist valve which will allow low speed operation of the hoist or jack under high thrust or load conditions, and high speed operation under low thrust or load conditions.

In certain uid pressure control systems for selectively controlling the operation of a -iiuid pressure-operated hoist or jack, it is ydesirable from the standpoint of conservation of fluid energy and speed of operation to include suitable means which will permit low speed operation of the hoist or jack under high thrust or load conditions, and high speed operation under low thrust or load conditions. While this problem may be presented in many different arts, an understanding of the invention will be facilitated by reference to the problem in a specic environment in which the invention is intended to be used primarily.

Thusly, and referring specically to the earth-moving art, a single acting hoist is commonly utilized ywith earthmoving carryall Scrapers for lifting the scraper apron which closes the front of the scraper bowl thereby permitting the material in the bowl to be discharged therefrom. A scraper vehicle of this type is disclosed in the United States Patent to E. R. Fryer et al., No. 2,773,320. Referring to such a scraper construction, upon initially actuating the apron hoist or jack for the purpose of discharging material from the loaded bowvl, the jack is subjected to a relatively high load or thrust condition due to the weight of the material in the bowl bearing against a substantial portion of the apron. However, as soon as the lip of the apron is lifted a relatively short distance from the cutting edge `or mouth of the scraper bowl, some material is discharged and a substantial portion of the weight of the material in the bowl is relieved from the apron. At this time, the load on the hoist is decreased. In such an environment of varying thrust or load conditions, it is the purpose of the present invention to per-V mit the hoist or jack to initially act at a low speed under high load or thrust conditions, followed by high speed operation of the hoist after the load on the latter has been relieved to a certain extent.

` It is, therefore, a principal object and feature of this invention to provide a uid pressure control system for a fluid pressure-operated hoist or jack which will permit low speed operation of the hoist under high thrust or load conditions, and high speed operation under low thrust or load conditions in order to more efliciently utilize the energy in the uid system.

It is yet another object and feature of this invention to provide such a control system as aforedescribed which includes a high-low speed hoist valve means acting to control the interchange of working uid under pressure from one end of the hoistgor jack to the other to vary the effective force acting upon the hoist under varying load conditions.

It is yet another object and feature of this invention, according to a preferred embodiment of this invention, to provide such a high-low speed hoist valve means which is selectively manually operable to control the operation of the hoist in accordance with load or thrust conditions.

It is still another object and feature of this invention,

ICC

according to another embodiment of this invention, to provide such a valve means which is automatically responsive to variation rin load or thrust conditions to effecty are attained in a fluid pressure control system for a v single-acting fluid pressure-operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder for connection to a load, first conduit means for supplying fluid under pressure to the piston head side of the cylinder, second conduit means for exhausting uid from the rod side of the cylinder, a high-low speed hoist valve means which either permits or prevents the exhaust of fluid through said second conduit means as fluid under pressure is being supplied through said rst conduit means, and a third conduit means selectively communicating the rod side of the cylinder to the head side there- `of when the pressure is the former exceeds that in the latter due to the valve being in the Iflow-preventing position in the second or exhaust conduit means. Under high thrust or load conditions, the rod side of the hoist is vented to exhaust and the fluid delivered through the iirst conduit means acts upon an 'effective area equal to the area of the piston head for high thrust, Ilow speed hoist operation. After the high thrust condition passes, the aforementioned valve means is positioned to prevent exhaust of uid from the rod side of the cylinder through the second conduit means. Under these circumstances, the pressure of the `iiuid in the rod side of the cylinder exceeds that in the head side thereof causing fluid flow therebetween through the aforementioned third conduit means. Thus, the fluid being delivered through the first conduit means acts on an effective area of the piston head equal to the diameter of the piston rod for vhigh speed, low thrust hoist operation. According to a iirst conduit means which is indicative of load or thrust conditions. l

The foregoing objects and the manner in which they are attained will become more apparent hereinafter as the description of the invention proceeds, and in which reference is made to the following drawings in which:

FIGURE 1 is a sectional View of a fluid pressure control system employing a preferred embodiment of the invention with the valve means in a neutral position;

FIGURE 2 is an enlarged view of one of the valve spools of FIGURE 1, but with the spool adjusted' from its neutral position permitting fast operation or raising of the hoist under low thrust conditions;

FIGURE 3 is a view similar to FIGURE 2, but showing the position of the spool to permit slow operation or raising of the hoist under high thrust conditions;

FIGURE 4 is a view similar to FIGURES 2 and 3, but showing the position of the spool to reverse the operation of or lower the hoist; and

FIGURE 5 is a view of a fluid pressure control system for a hoist incorporating a second embodiment of the invention.

Referring now particularly to FIGURES 1 through 4, there is shown a iluid pressure control system for a hoist scraper application as aforementioned. To this end, the

numeral 2 generally indicates a fluid pressure-operated hoist or jack comprising a cylinder 4 having its lower end pivotally pinned at 6 to a suitable portion of the scraper vehicle, such as the dnaw bar or pull yoke thereof. The open upper end of the cylinder is adapted to receive for reeiprocation the piston comprising the piston head 8 and a piston rod 10 of reduced diameter providing an annular clearance area 12 between the inner wall of the cylinder and thel piston rod. The upper end of the piston rod extends out of the cylinder and is adapted to be pivotally connected at 14 `to the operating construction controlling the raising and lowering of the scraper apron. Naturally, the upper end of the cylinder is suitably sealed. A one-way spring-loaded check valve 16 is mounted within a passageway -18 communicating the head side of the cylinder 4 to the clearance area 12 yor -rod side thereof for lluid interchange from the clearance area to the head side of the cylinder under certain operating conditions as will appear hereinafter.

The basic components of the uid system are completed by a reservoir or tank 20 containing uid adapted to be supplied by the pump 22 through the supply line 24 to an inlet port 26 in a valve assembly indicated generally at 28. An outlet or exhaust port 30 returns uid through the conduit 32 to the tank 20. The valve assembly 28 selectively controls the supply and exhaust of fluid from the lower or head end of the cylinder through the conduit 34, and the exhaust and supply of lluid to the rod side of the cylinder through the conduit 36.

The valve assembly 28 includes the valve body 38 in which the lluid inlet port 26 and exhaust port 30 previously described are formed, and three valve spool assemblies 40, 42 and 44 reciprocably disposed in the valve body 38 and selectively manually actuable to control porting to be described to control upto as many as three individu-al hoists or jacks. Thus, the valve spool assembly 40 controls the operation of the hoist 2, while it will be understood that connections similar to the conduits 34 and 36 may be made to the ports of the spool assemblies 42 or 44 or both to control other hoists. For example, in the particular environment in which this invention is intended to be used, the spool assembly 42 may be connected to the scraper bowl control jacks while the spool assembly 44 may be connected to the ejector operating jack.

The valve assembly 28 is of the open center type in that the valve body 38 includes a series of galleries or chambers 46, 48, S and 52 which are always in series communication with the respective valve spool assemblies in their neutral positions as shown in FIGURE l of the drawings. Thus, with the spool assemblies disposed in such a neutral position, uid entering the gallery ory charnber 46 may pass through the annular land 54 on the valve body about the spool assembly 40 into the -gallery or chamber 48, and then past the annular body land 56 into the gallery 50 to the annular body land 58 and into the gallery 52. The gallery 52 opens into a common exhaust gallery 60 at one end `of thervalve body 38 in free cornmunication with the exhaust port 30. Of course, fluid under pressure is supplied to the inlet gallery 46 from the inlet port 26 and flows freely about the conventional spring-biased relief valve 62. Therefore, with each spool assembly in the neutral position shown in FIGURE l, there is free flow of uid from the inlet port 26 through the various galleries aforementioned, which cumulatively constitute an inlet gallery for the group of spool assemblies, to the common exhaust gallery 60 and port 30 thereby providing free circulation of the fluid while none of the power devices connected to the valve assembly 28 are in operation. On the other hand, if one of the spool assemblies is actuated, as will appear more fully hereinafter, one of the valve body lands 54, 56 or 58 are closed thereby directing all available fluid under pressure to the ports associated with the valve spool being actuated.

In addition to the inlet gallery and common exhaust gallery aforedescribed, two additional exhaust galleries 64 and 66 are provided within the valve body in open communication with common exhaust gallery 6) and serving or being common to each of the three valve spool subassemblies 40, 42 and 44. Therefore, these inlet and exhaust gallery systems are common to each valve spool assmbly and serve the particular assembly being actuate Inasmuch as each of the three valve spool assemblies are structurally and functionally identical, further description will be directed to the `structure and operation of the valve spool assembly 4l) which controls the operation of the hoist 2.

Each valve spool assembly, and referring particularly to assembly 40, comprises an axially shiftable valve spool 68 comprising the axially spaced cylindrical valve lands 70, 72, 74, 76 and 78. It is important to note that the valve land 78 has its inner end charnfered or tapered as indicated at 80 for a purpose to appear hereinafter. Each valve spool is selectively manually shiftable within a bore in the valve body 38 which includes the annular valve body lands 82, 84, 86, 88, and 54, previously described.

A pressure outlet port 91 is in communication with the conduit 34 leading to the piston head side of the cylinder 4, while a second pressure outlet port 92 is connected through the conduit 36 to the rod side of the cylinder 4. A pressure inlet port 94 is formed between the aforementioned outlet ports and is adapted to be supplied with fluid under pressure from the inlet gallery 46 through the passage 96 and the one-way spring-biased check valve 98 mounted therein.

The valve spool land 70 cooperates with the valve body land 82 to control selected communication between the pressure port 91 and the exhaust gallery 66, while the valve spool vland 74 cooperates with the valve body land 88 to control similar communication between the other pressure port 92 and the exhaust gallery 64. The valve spool land 72 cooperates with one or the other of the valve body lands 84 and 86 to selectively direct lluid under pressure from the pressure inlet port 94 to one or the other of the outlet ports 91 or 92. The valve spool land 76 cooperates with the valve body land 54 to control the flow of uid from the inlet chamber or gallery 46 to the gallery 48 as aforedescribed, while the chamfercd land indicated at 80 under certain conditions of operation cooperates with the valve body land 54 to throttle the ow of fluid from the gallery 46 to the gallery 48, all of which will appear hereinafter.

It will be understood that each of the valve spools 68 -is provided with projecting ears 10G adapted to be suitably connected to a manually controlled lever for shifting the valve spool, there also being provided at the opposite end of each valve spood a conventional selfcentering spring construction -102 acting to maintain the valve spool in its normal or neutral position. As desired, but preferably, the upper end of the spool beyond the self-centering spring mechanism 102 is provided with a conventional detent -machanism 104 which serves to hold a particular valve spool in a selected position.

Inasmuch as the nature of the structure aforedescribed and the manner in which it functions to achieve the foregoing objects of this invention will become more apparent from a description of the operation of the construction, such description will now proceed with particular reference to the valve spool assembly 40` controlling the hoist 2, it being understood that each of the spool assemblies if connected to a similar hoist will function in an identical manner. lIn operation, the valve spool 68 will be disposed in its neutral position as shown in FIGURE l in which uid entering the inlet gallery 46 through the port 26 is free to flow through the remaining galleries which `are series connected to the common exhaust gallery 60 and the port 30 for return to the tank 30. It may be assumed that the hoist or jack 2 is connected to an apron closed over the mouth of a loaded scraper bowl.

To lift the apron under such high load or -thrust conditions, the valve spool 68 is shifted manually to the position shown in FIGURE 3 of the drawings in which the spool land 72 uncovers body land -84 to permit the flow or fluid under pressure from the pressure inlet port 94 to the pressure outlet port 91 and thence through the conduit 34 to the piston head side of the cylinder 4. As the spool is so moved, the spool land 76 closes upon the body land 54 to insure that all uid available in inlet gallery `46 is now directed through the passage 96 and past the spring-biased check valve 98 to the aforementioned pressure inlet port 94. One purpose of a check valve 98 controlling the flow through the passageway 96 is to insure that there is sufficiently high pressure in the inlet port 94 to move the hoist when the valve is initially operated; that is, the pump may not be delivering suiilcient pressure and a check valve construction insures that pump pressure will be built up for delivery to the pressure inlet port.

With the valve in the FIGURE 3 position, it will also be seen that the valve spool land 74 opens the valve body land 88 thereby permitting a free iiow of fluid from the pressure port 92 to the exhaust gallery 64. As a result, the rod side of the cylinder 4 is vented 'through the conduit 36. Consequently, the pressure on the head side of the piston is greater than that of the rod side thereof, and the spring-biased check valve 16 in the head of the piston remains closed and the fluid delivered through the conduit 34 acts upon the entire area of the piston head 8 thereby providing slow speed, high thrust operation of the hoist.

As the scraper apron breaks away from the bowl or the load on the hoist decreases, the valve spool 68 is shifted to the position shown in FIGURE 2. Under these circumstances, the porting remains the same except for engagement of the valve spool land 74 with the body land 88 thereby preventing venting of the rod side of the cylinder to the exhaust gallery 64. Consequently, as the piston continues to rise within its cylinder, the pressure of the fluid on the rod side Iof the cylinder within the clearance area 12 increases to a value in excess of that operating on the piston head side of the cylinder. Thus, there is fluid interchange or iluid flow from the rod side of the cylinder through the passage 18 and the one-way check Valve 16 to the head side thereof. Therefore, in this low thrust or low load condition, the entire volumetric capacity of the pump is, in effect, acting on an effective diameter of the piston head 8 which is equal to the diameter of the piston rod 10. Of course, this result is obtained because the fluid surrounding the piston rod is also delivered to the head side of the piston to augment the iiuid supply through the conduit I34. Consequently, the elfect is similar to directing a fixed volume of oil from a larger cylinder into a smaller cylinder thereby resulting in more rapid actuation of the hoist under the low thrust or load conditions.

When it is desired to lower 4the hoist 2, the valve spool 68 is shifted to the position shown in FIGURE 4. In this position, the valve spool land 70 opens communication from the pressure port 91 past the valve body land 82 to the exhaust gallery 66 thereby venting the head side of the cylinder. The piston rod then begins to move downwardly within its cylinder under the weight of the apron or other load connected thereto. During this cycle, the valve spool land 72 opens communication through body land 86 between the pressure inlet port 94 and the pressure port 92 communicating through the conduit 36 with the rod side of the cylinder for the purpose of filling the latter. To insure that the rod side of the cylinder is completely filled with yoil for subsequent operating cycles, it will be noted from FIGURE 4 that the chamfered land 80 forms a throttle across the valve body land 54 controlling the flow of uid from the gallery 46 to the gallery 48 of the valve body. As a consequence, pressure is built up in the gallery or chamber 46 to insure full fluid ow through the passageway 96 to the pressure inlet port 94 and the rod side of the hoist. Obviously, if the top or rod side of the hoist is not filled, there will not be suicient oil available for the fast raise or low thrust, high speed operation of the hoist as previously described.

After the hoist has been returned to the position shown in FIGURE 1, the spool may be released and thereby returned -to the neutral position shown in FIGURE 1. It should also be apparent that should the operator release the spool during any Ioperating cycle of the hoist, the valve spool will automatically be returned to the F-IG- URE 1 position thereby interrupting lany fluid ow between the valve assembly 28 and the hoist 2. The result is that the hoist piston will be held or retained in its extended position at that time.

Another embodiment of the invention is depicted in FIGURE 5, and comprises a single-acting hoist or jack 110 connected to a pressure line :112 which, in turn, isV

connected to -a fixed displacement pump 113 through a suitable control lor selector valve .114. The tank or reservoir 126 supplies the pump 113 and is also connected through the return or exhaust line 115 to the control valve 114. The hoist piston 116 is reciprocably disposed in the hoist cylinder 118, and is adapted to be connected to the load to be actuated. The rod side of the hoist cylinder -is connected by the line 120 to an automatically operable shuttle or high-low speed hoist valve construction indicated generally at 122.

The valve construction 122 comprises a valve body 128 in which the movable valve member 130 is axially 4 or tapered portion 140 on the smaller piston 132 to provide an overlap surface between the chambers .136 and 1138. The face of the piston 132 is continuously subjected to the pressure -of the fluid in conduit 112 by means `of the conduit 142. -The spring 144 normally urges the valve member to the position shown in the drawing in which the valve lands 146 and 147 prevent communication between the annular exhaust port 148 connected to the conduit .120 and the Aannular port 150 connected by the conduit 124 to the tank or reservoir .'126. However, in response to a predetermined pressure buildup occurring in the supply or delivery conduit 112 in -a manner to be described hereinafter, the valve member [130 may be shifted to the right in the drawing to collapse the spring 144 until the stop 152 abuts the wall of the valve body. At this time, the lands 146 and 147 will be in a position to communicate the annular ports 148 and 150 thereby venting the rod side of the piston to tank.

A small axial passage 154 through the valve member 130 communicates lwith a relieved portion 156 in the peripheral surface of piston member i134 adapted to selectively overlap and communicate with a similar relieved portion i158 in the chamber 1138. For a purpose to vappear more fully hereinafter, it may be noted that the relieved portions .140, 156 and 158 bear a particular relationship to-each other so as to selectively Icontrol the supply and exhaust of uid under pressure to and from the chamber 138 enclosing the piston member 134. Thus, it will be noted that with the valve member y130 in the position shown in FIGURE 5 of the drawings, the relieved or tapered portion of piston member 132 does not overlap the chamber 138 thereby preventing the pressure of the fluid in line 142 from acting on the face of the piston member 134. At the same time, however, the relieved portions I158 and 156 are in communication with each other so as to bleed or exhaust the chamber 138 through passage 154 in a manner to be described hereinafter. As the valve member 130 shifts to the right in the drawings, the relieved or tapered portion 140 will eventually overlap the chamber 138 thereby communieating the uid under pressure in conduit 142 with the face of the piston member 134. Concurrently wit-h this action, the relieved portion vi156 is moved to the right out of communication with the relieved portion 158 thereby preventing further bleeding or exhausting of the fluid under pressure in chamber 138. Conversely, as the valve member 130 moves from a position fully to the right in the drawings to the position shown in the drawings, the position will be reached in which communication between the relieved portions 156 and 158 is again obtained to bleed the chamber `138, while communication between the latter and the huid under pressure in conduit 142 is interrupted by piston 132.

A branch conduit 160 connects the vent conduit `120 to the pressure delivery conduit 112, and is provided with a one-way spring-loaded ball check valve 162. In somewhat similar fashion, the vent conduit l120 is connected by a branch conduit 164, including a one-way springloaded check valve 166, to the annular port 150 in the valve body. A transverse bore 168 in the valve member 130 intercepts the axial passage 154, and is adapted to communicate with the annular port 150 with the valve member 130 substantially in the position shown in the drawings.

In the operation, it may be assumed that the hoist or jack 110 is connected to a load such as a scraper apron closed over the mouth of a loaded scraper bowl. 'Ilo lift the apron against this high load under such high thrust conditions, the control or selector valve 114 is actuated to supply lluid through the pressure line 112 to the hoist piston head, it being understood that fluid is prevented from passing from the control valve i114 through the return line 1'15 to tank. For reasons aforementioned, a relatively large load is being imposed upon the hoist initially. As a consequence, the pressure in line 112 builds up and acts initially on the head or face of piston 132 to gradually move the valve 4member 130 against the spring 144. After a relatively small amount of such movement, the tapered or relieved portion 140 on the piston member 132 overlaps the chamber y138 while the relieved portion 156 on the piston member 134 moves out of communication with the relieved portion `158 in the chamber 138. As a result, the fluid under pressure in conduit 142 is now rapidly available to act against the face of piston 134 as well as against the face of piston `132. As a consequence, the valve member v130 moves rapidly Ito the right collapsing spring 144 until abutment of the stop 152 with the valve body. Thus, the right side of the hoist is vented to tank due to the uid interconnection `of the annular ports 148 and 150 respectively connected to the conduits 120 and 124. Under such high load conditions, the volumetric discharge from the pump acts upon the entire diameter of the piston head to slowly move the hoist with high thrust to break the apron away vfrom the bowl.

The valve member 130 remains in its shifted position or to the right in the drawing until such time as the pressure in the delivery line 112 -falls to a particular predetermined pressure. Thus, as the apron breaks away from the bowl and the -load lon the hoist decreases, the pressure in line 112 decreases permitting the spring 144 to move the valve member 130 to the left in the drawing toward its initial position. Eventually, the relieved portions or passages 156 and 158 are connected and the tapered or relieved portion 140 of piston member 132 no longer overlaps the chamber 138. Consequently, pressure in the chamber 138 will rapidly collapse inasmuch as chamber 138 has been shut off from supply from the conduit 142 and is being vented through the relieved portions 158 and i156, axial passage 154, transverse passage 168 and annular port 150 to the exhaust conduit 124. Thus, spring 144 rapidly shifts valve member 130 to the position shown in FIGURE 5 disrupting communication between annular ports 148 and 150 and venting both ends of the valve member to port 150 through passages 154 and 168. As the apron is lifted further, check valve 162 permits Huid to circulate from the rod side of the hoist into the line 112; in other words, pressure in line 120 will not exceed the pressure in line 112 ignoring friction losses, the weight of check valve 162, and the force of the spring associated with the latter. As a result of this low-thrust condition, the entire volumetric capacity of the pump is, in effect, acting on an effective diameter of the piston head equal to the diameter of the piston rod. This result is attained because the uid surrounding the piston rod is also being delivered to the pressure line 112 to augment that supplied from the pump. Consequently, as with the previously described embodiment, the effect is similar to directing a fixed volume of oil from a larger cylinder into a smaller cylinder thereby resulting in more rapid actuation of the hoist.

At this juncture, it should be noted that `the system aforedescribed is such that the fluid pressure required to shift valve member 130 from the position of FIGURE 5 to a venting position communicating ports 148 and 150 is greater than the pressure at which the valve member 130 is permitted to return to the position of FIGURE 5 under the influence of spring 144. Moreover, in order to prevent chatter or hunting of valve member 130, the ratio of the effective area of the face or head of piston -134 relative to the similar area of piston 132 is greater than the ratio of the area of the head of the hoist piston relative to the area of hoist piston rod 116. It is believed that the nature and purpose of this relationship will become more apparent from a consideration of the problem solved thereby.

Merely for the purpose of illustration, it may be assumed that the effective area of the hoist piston head is twice that of the rod 116. It may likewise be assumed that, due to an identical 2:1 ratio existing between the effective area of piston 134 relative to that of piston 132, the valve member 130 will be fully shifted to the right in response to a pressure `of 1000 p.s.i. in conduit 112, and will be returned to the position of FIGURE 5 when the pressure in conduit 112 falls to 500 p.s.i. Finally, let it be assumed that a pressure of 1000 p.s.i. is required to move the load attached to hoist with the valve member 130 in the position shown in FIGURE 5.

Thus, it will be seen that, after control valve 114 is actuated and after the pressure in conduit 112 builds up to 1000 p.s.i., valve member 130 will be shifted from the position of FIGURE 5 causing venting of the conduit to tank. Thereafter, due to the fact that the fluid under pressure in conduit 112 now acts on an effective area equal to the area of the hoist piston head which is twice that of the rod 116, only a pressure of 500 p.s.i. is required to move the load attached to hoist 110. As the pressure in conduit 112 then falls to 500 p.s.i., valve member moves back to the position of FIGURE 5 disrupting venting of conduit 120. Consequently, the fluid under pressure in conduit 112 must now act as an effective hoist piston area equal to the area of rod 116, and a pressure of 1000 p.s.i. is again required to move the load attached to hoist 110. It then becomes apparent that, as the pressure in conduit 1112 again builds up to 1000 p.s.i., valve member 130 is again shifted to vent conduit y120. Consequently, a new cycle begins and is repeated continuously. Under such circumstances, the result is that the valve member .130 will chatter or hunt to and fro between its extreme positions while the hoist L10 and the load attached thereto will remain substantially stationary.

Therefore, to solve this problem, the area ratio aforementioned between pistons 134 and 132 is preselected so as to bear a definite relationship to the ratio between the effective head and rod areas of hoist 110; that is, so that the valve member 130 cannot return from a shifted position to the position of FIGURE 5 until the pressure in conduit 112 reaches a predetermined value, such as 400 p.s.i., less than 500 p.s.i. in the foregoing example.

More specifically, to accomplish this end in the example given, the effective area of the piston 13'4 will be some preselected amount more than twice the effective area of piston 132; that is, the ratio of the aforementioned areas of pistons 1.134 and 13-2 is greater than the 2:1 ratio of the hoist piston head and rod. Consequently, under slow speed-high thrust-conditions of the hoist 110 as aforedescribed, the valve member y130 -will shift to vent conduit 120 at 1000 p.s.i. and only 500 p.s.i. pressure will then be required to continue moving the load attached to hoist 110. Since this 500 p.s.i. pressure exceeds the 400 p.s.i. at which valve member 130 will return to the posi- -tion of IFIGURE 5, the valve member 130 remains in the shifted position and the hoist continues to move. When the load on the hoist decreases to the point at which the pressure in conduit 112 reaches 400 p.s.i., the valve member 130 will return to the position of FIGURE 5 and the hoist will continue to move.

When the hoist is to be 4returned to its fully retracted position, the control valve 114 is actuated -to exhaust the head side of the hoist through the conduit 112 and return conduit 1115 to tank 126. As the hoist is so retracted, make-up oil flows into the annular port 150 from the conduit 1124, into conduit 164 and past check valve 166 into the rod side -of the hoist as the latter is moved to a retracted position by the weight of the load attached thereto. The system is then in condition yfor a repeat cycle of operation as aforedescribed.

While two forms of the invention have been selected for an illustration thereof, other -forms will now be apparent to those skilled in the art. Therefore, the embodiments shown in the drawings are merely for illustrative purposes, and are not intended to limit the scope of the invention which is defined by the claims which follow.

I claim:

l. In combination, a fluid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder, means permitting iluid llow from the piston rod side of said cylinder to the piston head side thereof when the pressure of the fluid in the former exceeds that in the latter, and means controlling the pressure on the rod side of said cylinder relative to the pressure on the piston head side thereof to cause the pressure in the former to exceed that in the latter for lluid flow therebetween.

l 2. In combination, a uid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder, conduit means for supplying lluid under pressure to the piston head side of said cylinder and exhausting uid from the rod side thereof, means permitting iluid flow from the piston rod side of said cylinder to the piston head side thereof when the pressure of the iluid in the former -exceeds that in the latter, and valve means controlling the flow of fluid through said conduit means whereby the pressure on the rod side of said cylinder may exceed that on the piston head side thereof for iluid flow therebetween.

3. In combination, a uid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder, means permitting fluid flow from the piston rod side Kof said cylinder to the piston head side thereof when the pressure of the uid in the former exceeds .that in the latter, exhaust conduit means connected to the rod side of said cylinder, and valve means controlling the ow of fluid throughl said exhaust conduit means and having a position restricting fluid flow therethrough to cause the pressure on the rod side of said cylinder to exceed the pressure on the piston head side thereof.

4. In combination, a fluid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder, means including one-Way valve means permitting iluid ow yfrom the piston rod side of said cylinder to the piston head side thereof when the pressure of the iluid in the former exceeds that in the latter, and means controlling the pressure on the rod side of said cylinder relative to the pressure on the piston head side thereof to cause the pressure in the Iformer to exceed that in the latter for fluid ilow through said valve means.

5. In combination, a lluid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder,vconduit means communicating the piston rod side of said cylinder with the piston head side thereof, one-way check valve means in said conduit means permitting lluid ow from the piston rod side o-f said cylinder to the piston head side thereof when the pressure of the fluid in the for-mer exceeds that in the latter, exhaust conduit means connected to the rod side of said cylinder, and valve means controlling the flow of lluid through said exhaust conduit means to cause the pressure on the rod side .of said cylinder to exceed that on the head side thereof for fluid ow through said check valve means.

`6i. In combination, a flu-id pressure operated jack comprising a cylindenpa piston reciprocably disposed within said cylinder and including a piston head and 'a piston rod rigidly secured thereto and extending out of Said cylinder, first conduit means for supplying fluid under pressure to the piston head yside of said cylinder, second conduit means connecting the rod side of said cylinder to exhaust, valve means `controlling the flow of fluid through said second conduit means, said valve means having one position preventing fluid flow through said second conduit means and another position permitting such fluid flow, and means permitting uid llow from the piston rod side of lsaid cylinder to lthe piston head side thereof when the pressure of the fluid in the former exceeds that in the latter `with said valve means in said one position.

7. In combination, a fluid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and la piston rod rigidly secured thereto and extending out of said cylinder, Iiirst conduit me-ans for supplying fluid under pressure to the piston head side of said cylinder, second conduit means connecting the rod side of said cylinder to exhaust, iirst valve means controlling the ow of iluid through said second conduit means, said lirst valve means having one position preventing iluid flow through said second conduit means and another position permitting such flow, and third conduit means including second valve means permitting iluid flow from the piston rod side of said cylinder to the piston head side thereof when the pressure of the fluid in the former exceeds that in the latter with said rst valve means in said one position. 8. In combination, 'a fluid pressure yoperated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder, first conduit means for supplying fluid under pressure to the piston head side of said cylinder, second conduit means connecting the rod side of said cylinder t-o exhaust, valve means controlling the ow of duid through both said rst and second conduit means, said valve means having a one position permitting duid ilow through said first conduit means and preventing fluid ow through said second conduit means and another position permitting iluid ilow through both the first and `second conduit means, and means permitting uid flow from the piston rod side of said cylinder to the piston head side thereof when the pressure of the fluid in the former exceeds that in the latter with said valve means in said one position.

1 1 9. In combination, a fluid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder, first conduit means for supplying fluid under pressure to the piston head side of said cylinder, second conduit means connecting the rod side of said cylinder to exhaust, first valve means controlling the flow of fluid through both said first and said conduit means, said first valve means having one position permitting fluid flow through said first conduit means and preventing fluid ow through said second conduit means and another position permitting tiuid flow through both the firs-t and second conduit means, and third conduit means including second valve means permitting uid flow from the piston rod side of said cylinder to the piston head side thereof when the pressure of the fluid in the former exceeds that in the latter with said first valve means in said one position. v

10. In combination, a fluid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto `and extending `out of said cylinder, a passageway in said piston head communicating the piston rod side of said cylinder to the piston head side thereof, one-way check valve means in said passageway permitting fluid flow from the piston rod side of said cylinder to the piston head side thereof when the pressure in the former exceeds that in the latter; a selector valve comprising Ia valve body, 1a fluid pressure inlet port Iin said body, an exhaust port in said body, a rst pressure port in said body communicating with the piston head side of said cylinder, a second pressure port in said body communicating with the rod side of said cylinder, and a movable valve member in said body selectively controlling communication between said respective ports, said valve member having a first position communicating ysaid first pressure port with said inlet port and preventing duid flow through said second pressure port thereby causing the pressure in the rod side of said cylinder to exceed that in the piston head side thereof and fluid to flow through said passageway, and a second position communicating said first pressure port with said inlet port and said second pressure port with said exhaust pont whereby the pressure of the fluid on the rod side of said cylinder is maintained below that in .the piston head side thereof.

l1. `In combination, a fluid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder, a passageway in said piston head communicating the piston yrod side of said cylinder to the piston head side thereof, one-Way check valve means in said passageway permitting fluid ow from the piston rod side of said cylinder to the piston head side thereof when the pressure in the former exceeds that in the latter; a selector valve comprising a valve -body including a fluid pressure inlet gallery, a fluid pressure inlet port in said body and connected to said gallery, an exhaust port in said body, a rst pressure port in said body communicating with the piston head side of said cylinder, a second pressure port in said body communicating with the rod side of said cylinder, a movable valve member in said body selectively controlling communication between said respective ports, said valve member having a first position communicating said first pressure port with said inlet port and preventing fluid flow through said second pressure port thereby causing the pressure in the rod side of said cylinder to exceed that in the piston head side thereof and fluid to flow through said passageway, and a second position communicating said rst pressure port with said inlet port and said second pressure port with said exhaust port whereby the pressure of the fluid on the rod side of said cylinder is maintained below that in the piston head side thereof, said valve member having a third position communicating said first pressure port with said exhaust port and said second pressure port with said inlet port, and throttle means on said valve member throttling the flow of fluid from said inlet gallery to said exhaust port to insure substantially full flow from said inlet gallery to said inlet port and second pressure port with said valve member in said third position.

12. In combination, a fluid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder, first conduit means communicating the piston rod side of said cylinder with the piston head side thereof, one-way check valve means in said first conduit means permitting fluid flow from the piston rod side of said cylinder to the piston head side thereof when the pressure in the former exceeds that in the latter, second conduit means communicating fluid under pressure to the piston head side of said cylinder, third conduit means communicating the rod side of said cylinder to exhaust, a valve assembly in said third conduit means and including a lmovable valve member controlling the flow of uid under pressure therethrough, said valve member having a neutral position preventing uid flow through said third conduit means and a shifted position permitting flow therethrough, and means communicating said second conduit meansto said valve member to move the latter automatically to said shifted position at a predetermined pressure in said second conduit means.

13. In combination, a fluid pressure operated jack comprising a cylinder, a piston reciprocably disposed within said cylinder and including a piston head and a piston rod rigidly secured thereto and extending out of said cylinder, first conduit means communicating fluid under pressure to the piston head side of said cylinder, second conduit means communicating the rod side of said cylinder to exhaust, a valve assembly in said second conduit means `and including a Huid pressure responsive movable valve member controlling the ow of uid under pressure therethrough, said valve member having a neutral position preventing fluid flow through said second conduit means and a shifted position permitting flow therethrough, means communicating said first conduit means to said valve member to move the latter automatically to said shifted position at predetermined pressure in said first conduit means, and means permitting one-way ow of uid from said second conduit means to said first conduit means from the pressure in the former exceeds that in the latter with said valve member in the neutral position.

References Cited in the file of this patent UNITED STATES PATENTS 2,283,124 Peterson et al. May 12, 1942 2,563,295 Westbury Aug. 7, 1951 2,751,822 Schlitz June 26, 1956 2,868,227 Stephens Ian. 13, 1959 2,898,891 Gusching et al. Aug. 1l, 1959 2,949,097 Vander Kaay Aug. 16, 1960 2,965,133 Rice et al. Dec. 20, 1960 FOREIGN PATENTS 1,075,362 France Apr. 14, 1954 

10. IN COMBINATION, A FLUID PRESSURE OPERATED JACK COMPRISING A CYLINDER, A PISTON RECIPROCABLY DISPOSED WITH SAID CYLINDER AND INCLUDING A PISTON HEAD AND A PISTON ROD RIGIDLY SECURED THERETO AND EXTENDING OUT OF SAID CYLINDER, A PASSAGEWAY IN SAID PISTON HEAD COMMUNICATING THE PISTON ROD SIDE OF SAID CYLINDER TO THE PISTON HEAD SIDE THEREOF, ONE-WAY CHECK VALVE MEANS IN SAID PASSAGEWAY PERMITTING FLUID FLOW FROM THE PISTON ROD SIDE OF SAID CYLINDER TO PISTON HEAD SIDE THEREOF WHEN THE PRESSURE INTHE FORMER EXCEEDSS THAT IN THE LATTER; A SELECTOR VALVE COMPRISING A VALVE BODY, A FLUID PRESSURE INLET PORT IN SAID BODY, AN EXHAUST PORT IN SAID BODY, A FIRST PRESSURE PORT IN SAID BODY COMMUNICATING WITH THE PISTON HEAD SIDE OF SAID CYLINDER, A SECOND PRESSURE PORT IN SAID BODY COMMUNICATING WITH THE ROD SIDE OF SAID CYLINDER, AND A MOVABLE VALVE MEMBER IN SAID BODY SELECTIVELY CONTROLLING COMMUNICATION BETWEEN SAID RESPECTIVE PORTS, SAID VALVE MEMBER HAVING A FIRST POSITION COMMUNICATING SAID FIRST PRESSURE PORT WITH SAID INLET PORT AND PREVENTING FLUID FLOW THROUGH SAID SECOND PRESSURE PORT THEREBY CAUSING THE PRESSURE IN THE ROD SIDE OF SAID CYLINDER TO EXCEED THAT IN THE PISTON HEAD SIDE THEREOF AND FLUID TO FLOW THROUGH SAID PASSAGEWAY, AND A SECOND POSITION COMMUNICATING SAID FIRST PRESSURE PORT WITH SAID INLET PORT AND SAID SECOND PRESSURE PORT WITH SAID EXHAUST PORT WHEREBY THE PRESSURE OF THE FLUID ON THE ROD SIDE OF SAID CYLINDER IS MAINTAINED BELOW THAT IN THE PISTON HEAD SIDE THEREOF. 